Present-day types of concrete, including HPC (High Performance Concrete) and SCC (Self Compacting Concrete), contain a relatively high amount of fines to ensure an adequate resistance against segregation. In some instances, a high amount of fines is essential from a wish to obtain a certain imperviousness of the construction to water. The amount of fines originates from cement, possibly fly ashes, micro silica etc., and to a smaller extent, from the sand and gravel materials.
There is both a widespread economic and technical need of reducing this amount of fines. For one thing, the amount of fines in concrete and mortar to a large extent adds up to the costs of these materials, and for another, there is a considerably technical need of obtaining improved properties of concrete and mortar in fresh as well as in hardened condition. The improved properties are i.a. of a rheological nature. Furthermore it is desirable that concrete and mortar must be self-compacting, whereby these materials should show extreme high flow, and ability to fill as well as internal stability, in order that the material is not segregated in a water and powder phase.
The closest related prior art is described in DK 173458 B1. This reference discloses a segregation robust, self-leveling, self-compacting concrete with “High Performance” properties. This concrete is manufactured by adding 2-10% of palygorskite or sepiolite having a length/diameter ratio (aspect ratio) of more than 35. The purpose of adding palygorskite or sepiolite is to counteract or reduce defects or flaws, which may occur during hardening of especially High Performance concretes. As palygorskite increases the viscosity of the concrete and thereby deteriorates the flow properties, high doses of a superplasticizer are required. The defects and flaws stated are related to the concrete during hardening only and can be binding defects between paste/aggregate/reinforcement, irregularities in the structure of the paste, microscopic and macroscopic shortcomings, non-uniform distribution of the coarse aggregate, poor quality of the air void system and lack of hydration of cement grains locally in the cement paste. In DK 173458 B1, it is furthermore mentioned that when using laminar silicate minerals, including smectite, the desired effect, as provided when using palygorskite, is not obtained. A disadvantage of this prior art is that it is necessary to use higher levels of cost-increasing superplasticizers in order to obtain the desired effect of palygorskite.
Another disadvantage of using palygorskite is that it has been found to be carcinogenic in animal studies (cf. e.g. IARC Monographs Programme on the Evaluation of Carcinogenic Risks to Humans, vol: 68 (1997) (p245)).
EP 0467483 A1 discloses a method of making a stone foundation being impervious to water. By this prior art method, a mixture of graded aggregate (sand and gravel), mineral binder, bentonite and water is prepared. The bentonite used is preferably an activated bentonite and can be used as a dry additive or as a slurry in water after swelling for up to 24 hours. The mixture of the aggregate, mineral binder, bentonite and water requires the use of compaction to a degree of compaction of at least Proctor 98%, using e.g. a roller.
U.S. Pat. No. 3,832,193 discloses a refractory composition comprising refractory particles, water, diammonium phosphate and an acid or acid salt mixed therewith in an amount to give a pH below 7 and not less than 3. As refractory particles are mentioned i.a. bentonite. Diammonium phosphate liberates vapours of ammonia when the material is wet or damp. The liberation of vapours of ammonia is prevented by adjusting the pH of the mixture to a value below 7.
US 2004/0016369 A1 relates to smectite slurries including slurries of bentonite which are fully activated by ion exchange with sodium ions, said slurries comprising one or more phosphonate additives in an amount of 0.5-15% by weight based on the weight of smectite. In US 2004/0016369 A1, it is furthermore stated that said slurries are useful in self-leveling cement floors and in pumpable concrete systems to prevent settling of aggregates and excessive bleeding.
None of these references, neither alone nor in combination, anticipate an additive for a self-compacting concrete or mortar which allows the reduction of the amount of fines in said concrete or mortar by preventing the tendency of segregation of such concretes or mortars.
The object of the present invention is to improve the rheological properties of the self-compacting concretes and the mortars in fresh as well as in setting condition, i.e. from the time of mixing until final setting occurs, typically after 5-10 hours at 20° C.
Another object of the present invention is to prepare a self-compacting concrete or mortar with a reduced amount of fines and with a reduced content of superplasticizers.
A further object of the present invention is to avoid any health risks, which may be connected to the use of palygorskite.
Surprisingly, it has now been found that the above can be achieved by adding a small amount of additive according to the invention during the mixing of concrete or mortar having a reduced amount of fines. In this manner, a self-compacting concrete or mortar is prepared, which is resistant to segregation, so that the concrete or the mortar is not segregated in a water and powder phase.
Furthermore, it has surprisingly been found that the use of the additive according to the invention when mixing concrete and mortar results in a number of advantages of both an economic as well as an applied technical nature. These advantages can be characterised as follows:                1. By the use of the additive according to the invention, the amount of fines can be reduced resulting in a reduced cost price for the concrete.        2. The additive makes it possible to prepare robust self-compacting concretes (SCC) within all strength classes with a typical flow diameter >640 mm.        3. The additive according to the invention makes it possible to prepare robust self-compacting construction concretes (for vertical and/or complicated castings with closely spaced reinforcement) with extreme flow properties (flow diameter >700 mm).        4. The additive according to the invention provides concrete and mortar with a high internal stability so that the concrete or mortar tolerates higher pumping pressures without separating into a water and solid phase.        5. The additive according to the invention improves the rheology of concrete and mortar so that a minor variation of the water content does not influence the consistency.        6. The additive according to the invention ensures that the concrete or mortar product shows stable, plastic viscosity, i.e. a greater robustness.        7. When added to concretes or mortars, the additive according to the invention can eliminate the segregation, where segregation has already been observed, the additive according to the invention functioning as a kind of “repair material”.        8. The additive according to the invention provides concretes prepared with white Portland cement with considerably improved rheologic properties, which until now has not been possible.        